Interval Identification | Perfect Fifths (5 of 10)
Called Perfect for the same reason as an interval of a Perfect fourth, the ratio of the vibrational frequency of an interval of a Perfect fifth is 3/2. This means that an interval of a Perfect fifth above any given note vibrates at a frequency of one and a half more than the original note.
In other words, if a note vibrates at a frequency of two hundred hertz, or two hundred cycles, per second, then an interval of a Perfect fifth above that note would vibrate at a frequency of three hundred cycles per second.
Put more simply, an interval of a Perfect fifth occurs when any two notes are separated by the distance of seven consecutive half steps. Because two half steps equals one whole step, seven consecutive half steps can also be looked at as being comparatively the same as three whole steps and one half step.
Using this pattern of steps, let's see if we can figure out what an interval of a Perfect fifth above the note C is.
Starting on the note C and going up one whole step takes us to the note D.